Syntax

UND{cond}{.W} {#expr}

where:

cond

is an optional condition code.

.W

is
an optional instruction width specifier.

expr

evaluates to a numeric value. Table 13 shows the range
and encoding of expr in the
instruction, where Y shows the locations of the bits that encode
for expr and V
is the 4 bits that encode for the condition code.

If expr is omitted,
the value 0 is used.

Table 13. Range and encoding of expr

Instruction

Encoding

Number of bits for expr

Range

ARM

0xV7FYYYFY

16

0-65535

32-bit Thumb

0xF7FYAYFY

12

0-4095

16-bit Thumb

0xDEYY

8

0-255

UND in Thumb code

You can use the .W width specifier to force UND to
generate a 32-bit instruction in Thumb code on ARMv6T2 and above
processors. UND.W always generates a 32-bit instruction,
even if expr is in
the range 0-255.

Disassembly

The encodings that this pseudo-instruction produces disassemble
to DCI.